The invention relates to a starting material for the manufacture of electrical contacts which is made by resistance welding the starting material to an electrically conductive contact support consisting essentially of copper. The starting material is a laminated metal strip which has parallel ridges tapering from their base to their crest, formed on the side of the strip which is to be bonded to the contact support. The invention also relates to a method for the manufacture of a semi finished product for electrical contacts, and use of the semifinished product.
U.S. Pat. No. 4,342,893 discloses a starting material for the manufacture of electrical contacts by bonding to an electrically conductive metal contact support by resistance heating, wherein he starting material is in the form of a metal strip. The surface at which he metal strip is to be joined to the contact support has ridges running lengthwise of the metal strip at a distance apart, between which there are valleys which contain solder material; by means of this solder material an electrically conductive and mechanically strong bond is produced by resistance heating between the metal strip which serves as the continuous contact material and the strip which serves as the contact support.
DE-OS 31 07 665 discloses a metal semi-finished product with a strip-like support and a metal overlay, in which the support has on the side facing the overlay elevations and depressions which are covered with an intermediate layer serving as a solder layer. The overlay is bonded to the support by this intermediate layer by resistance welding or soldering.
DE-OS 34 37 981 discloses a method for the manufacture of a semi-finished product for electrical contacts, which consists of a metal contact support strip and a strip applied to it and then resistance welded onto it as the contact material. The strips serving as the contact material have one or more grooves on their side facing the support strip, into which so-called solder strands are separately laid before the resistance welding is performed, and after that they provide a strong bond between the contact support strip and the strip of contact material.
In the miniaturization of components--including contact elements for example--materials of higher electrical conductivity are increasingly being used, which on the one hand involve only slight losses of heat in operation, but on the other hand, due to their high heat conductivity they are difficult to weld or solder. Reference is made to these problems in British Patent No. 1,111,478. Furthermore it is extremely problematic Lo apply the external electrodes for resistance heating without damaging the semimanufactured contact material, especially the noble metal contact layer on the contact material, because even in these transitional areas a great amount of heat is developed which can result in the destruction of the surfaces of the semimanufactured product. Therefore, as the conductivity of the materials of the contact support and contact material increases, it proves to be difficult, on account of the poor bonding and welding possibilities, to produce a reliable and electrically and mechanically strong bond.
Furthermore, the separate feeding of solder material, as disclosed in DE-OS 34 37 981, involves considerable difficulty in practice in the application of separate contact points, such as contact points for relays.